The extremely productive nature of hydrothermal vent communities
puzzled scientists at first. Only certain organisms, known as primary producers, can
process energy from strictly inorganic sources. These primary producers
provide the organic compounds that other organisms need for growth
and energy. Sunlight usually provides the energy for the production
of organic compounds from inorganic compounds. Before hydrothermal
vents were discovered, prevailing opinion held that deep-sea communities
relied on the slow fallout of organic matter from the ocean's surface.
At the surface sufficient sunlight penetrates to allow photosynthesis
to occur, but even in the clearest waters there is not enough light
to fuel photosynthesis much below 100-200 meters deep.
Ecologists have traditionally looked to photosynthetic processes
as the ultimate source of energy that fueled aquatic food webs.
However, most of the organic compounds from surface waters are
consumed before they can penetrate to deep ocean waters. Consequently,
photosynthetic fallout could not account for the level of biomass
observed at venting sites. An alternative explanation was needed
to account for hydrothermal community productivity. Instead of
relying on photosynthesis, the vent food chain is built on the
basis of chemosynthesis.
Hydrothermal vents have taught us that chemosynthetic microorganisms can serve as primary producers without the aid of sunlight. At vents and methane seeps, high concentrations of hydrogen sulfide or methane can provide microorganisms with the chemical energy to synthesize organic compounds (Childress & Fisher, 1992). While scientists had recorded chemosynthetic processes as early as 1887 (Jannasch, 1997), it took the discovery of hydrothermal vents to highlight how important this process could be.
A particularly intriguing aspect of chemosynthesis at hydrothermal vents is the symbiosis that exists between bacteria and some vent organisms. A range of vent organisms, including tubeworms, mussels, and clams, host symbiotic bacteria inside their bodies. Symbiotic bacteria living within an organism are known as endosymbionts. Episymbionts, or symbiotic bacteria living on the exterior of animals, are found on hydrothermal polychaete worms and shrimp.
GO TO Organism adaptations to vent environments
List of Visuals
- Tube worm symbionts
Microbe Zoo (Comm Tech Lab and the Center for Microbial Ecology at Michigan State University, 253 Communication Arts & Sciences, Michigan State University, East Lansing, MI 48824-1212)